The additive manufacture of compositionally graded Al/Cu parts by laser engineered net shaping (LENS) is demonstrated. The use of a blue light build laser enabled deposition on a Cu substrate. The thermal gradient and rapid solidification inherent to selective laser melting enabled mass transport of Cu up to 4 mm from a Cu substrate through a pure Al deposition, providing a means of producing gradients with finer step sizes than the printed layer thicknesses. Divorcing gradient continuity from layer or particle size makes LENS a potentially enabling technology for the manufacture of graded density impactors for ramp compression experiments. Printing graded structures with pure Al, however, was prevented by the growth of Al2Cu3 dendrites and acicular grains amid a matrix of Al2Cu. A combination of adding TiB2 grain refining powder and actively varying print layer composition suppressed the dendritic growth mode and produced an equiaxed microstructure in a compositionally graded part. Material phase was characterized for crystal structure and nanoindentation hardness to enable a discussion of phase evolution in the rapidly solidifying melt pool of a LENS print.
This data documentation report describes geologic and hydrologic laboratory analysis and data collected in support of site characterization of the Physical Experiment 1 (PE1) testbed, Aqueduct Mesa, Nevada. The documentation includes a summary of laboratory tests performed, discussion of sample selection for assessing heterogeneity of various testbed properties, methods, and results per data type.
A thermally driven, micrometer-scale switch technology has been created that utilizes the ErH3/Er2O3 materials system. The technology is comprised of novel thin film switches, interconnects, on-board micro-scale heaters for passive thermal environment sensing, and on-board micro-scale heaters for individualized switch actuation. Switches undergo a thermodynamically stable reduction/oxidation reaction leading to a multi-decade (>11 orders) change in resistance. The resistance contrast remains after cooling to room temperature, making them suitable as thermal fuses. An activation energy of 290 kJ/mol was calculated for the switch reaction, and a thermos-kinetic model was employed to determine switch times of 120 ms at 560 °C with the potential to scale to 1 ms at 680 °C.
The cis- form of diaminodibenzocyclooctane (DADBCO, C16H18N2) is of interest as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein.
Researchers have the potential to be exposed to a wide variety of hazards inherent to the equipment they use and maintain. When equipment does not function as expected, researchers sometimes reach out to their vendors for assistance. Early diagnostic or troubleshooting interactions between researcher and vendor are often conducted over the telephone and can lead to researchers performing work outside of their area of expertise and exposure to unknown hazards. This type of interaction significantly contributed to an incident where during diagnostic activities a researcher accidentally contacted, and discharged, a capacitor in an X-ray diffraction instrument. While this incident did not produce a serious injury, if the capacitor discharge path had occurred hand-to-hand across the heart, a serious injury may have been possible.
Pb-Zr-Ti-O (PZT) perovskites span a large solid-solution range and have found widespread use due to their piezoelectric and ferroelectric properties that also span a large range. Crystal structure analysis via Rietveld refinement facilitates materials analysis via the extraction of the structural parameters. These parameters, often obtained as a function of an additional dimension (e.g., pressure), can help to diagnose materials response within a use environment. Often referred to as in-situ studies, these experiments provide an abundance of data. Viewing structural changes due to applied pressure conditions can give much-needed insight into materials performance. However, challenges exist for viewing/presenting results when the details are inherently three-dimensional (3D) in nature. For PZT perovskites, the use of polyhedra (e.g., Zr/Ti-O6 octahedra) to view bonding/connectivity is beneficial; however, the visualization of the octahedra behavior with pressure dependence is less easily demonstrated due to the complexity of the added pressure dimension. We present a more intuitive visualization by projecting structural data into virtual reality (VR). We employ previously published structural data for Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 as an exemplar for VR visualization of the PZT R3c crystal structure between ambient and 0.62 GPa pressure. This is accomplished via our in-house CAD2VR™ software platform and the new CrystalVR plugin. The use of the VR environment enables a more intuitive viewing experience, while enabling on-the-fly evaluation of crystal data, to form a detailed and comprehensive understanding of in-situ datasets. Discussion of methodology and tools for viewing are given, along with how recording results in video form can enable the viewing experience.
Herein, we report the synthesis of a novel, tetraphenylethylene-based ligand for metal-organic frameworks (MOFs). Incorporation of this ligand into a Zn- or Eu-based MOF increased the quantum yield (QY) by almost 2.5× compared to the linker alone. Furthermore, the choice of guest solvent impacted the QY and solvatochromatic response. These shifts are consistent with solvent dielectric constant as well as molecular polarizability.
Two novel LiCl·DMSO polymer structures were created by combining dry LiCl salt with dimethyl sulfoxide (DMSO), namely, catena-poly[[chloridolithium(I)]-μ-(dimethyl sulfoxide)-κ2 O:O-[chloridolithium(I)]-di-μ-(dimethyl sulfoxide)-κ4 O:O], [Li2Cl2(C2H6OS)3] n , and catena-poly[lithium(I)-μ-chlorido-μ-(dimethyl sulfoxide)-κ2 O:O], [LiCl(C2H6OS)] n. The initial synthesized phase had very small block-shaped crystals (<0.08 mm) with monoclinic symmetry and a 2 LiCl: 3 DMSO ratio. As the solution evaporated, a second phase formed with a plate-shaped crystal morphology. After about 20 minutes, large (>0.20 mm) octahedron-shaped crystals formed. The plate crystals and the octahedron crystals are the same tetragonal structure with a 1 LiCl: 1 DMSO ratio. These structures are reported and compared to other known LiCl·solvent compounds.
Niobium doped lead-tin-zirconate-titanate ceramics near the PZT 95/5 orthorhombic AFE – rhombohedral FE morphotropic phase boundary Pb1-0.5y(Zr0.865-xTixSn0.135)1-yNbyO3 were prepared according to a 22+1 factorial design with x = 0.05, 0.07 and y = 0.0155, 0.0195. The ceramics were prepared by a traditional solid-state synthesis route and sintered to near full density at 1250°C for 6 h. All compositions were ∼98% dense with no detectable secondary phases by X-ray diffraction. The ceramics exhibited equiaxed grains with intergranular porosity, and grain size was ∼5 µm, decreasing with niobium substitution. Compositions exhibited remnant polarization values of ∼32 µC/cm2, increasing with Ti substitution. Depolarization by the hydrostatic pressure induced FE-AFE phase transition was drastically affected by variation of the Ti and Nb substitution, increasing at a rate of 113 MPa /1% Ti and 21 MPa/1% Nb. Total depolarization output was insensitive to the change in Ti and Nb substitution, ∼32.8 µC/cm2 for the PSZT ceramics. The R3c-R3m and R3m-Pm3m phase transition temperatures on heating ranged from 90 to 105°C and 183 to 191°C, respectively. Ti substitution stabilized the R3c and R3m phases to higher temperatures, while Nb substitution stabilized the Pm3m phase to lower temperatures. Thermal hysteresis of the phase transitions was also observed in the ceramics, with transition temperature on cooling being as much as 10°C lower.
This report is the final documentation for the one-year LDRD project 226360: Simulated X-ray Diffraction and Machine Learning for Optimizing Dynamic Experiment Analysis. As Sandia has successfully developed in-house X-ray diffraction tools for study of atomic structure in experiments, it has become increasingly important to develop computational analysis methods to support these experiments. When dynamically compressed lattices and orientations are not known a priori, the identification requires a cumbersome and sometimes intractable search of possible final states. These final states can include phase transition, deformation and mixed/evolving states. Our work consists of three parts: (1) development of an XRD simulation tool and use of traditional data science methods to match XRD patterns to experiments; (2) development of ML-based models capable of decomposing and identifying the lattice and orientation components of multicomponent experimental diffraction patterns; and (3) conducting experiments which showcase these new analysis tools in the study of phase transition mechanisms. Our target material has been cadmium sulfide, which exhibits complex orientation-dependent phase transformation mechanisms. In our current one-year LDRD, we have begun the analysis of high-quality c-axis CdS diffraction data from DCS and Thor experiments, which had until recently eluded orientation identification.
Negative and zero coefficient of thermal expansion (CTE) materials are of interest for developing polymer composites in electronic circuits that match the expansion of Si and in zero CTE supports for optical components, e.g., mirrors. In this work, the processing challenges and stability of ZrW2O8, HfW2O8, HfMgW3O12, Al(HfMg)0.5W3O12, and Al0.5Sc1.5W3O12 negative and zero thermal expansion coefficient ceramics are discussed. Al0.5Sc1.5W3O12 is demonstrated to be a relatively simple oxide to fabricate in large quantity and is shown to exhibit single phase up to 1300 °C in air and inert N2 environments. The negative and zero CTE behavior was confirmed with dilatometry. Thermal conductivity and heat capacity were reported for the first time for HfMgW3O12 and Al0.5Sc1.5W3O12 and thermal conductivity was found to be very low (~0.5 W/mK). Grüneisen parameter is also estimated. Methods for integration of Al0.5Sc1.5W3O12 with other materials was examined and embedding 50 vol% of the ceramic powder in flexible epoxy was demonstrated with a commercial vendor.
Dirac semimetals have attracted a great deal of current interests due to their potential applications in topological quantum computing, low-energy electronic devices, and single photon detection in the microwave frequency range. Herein are results from analyzing the low magnetic (B) field weak-antilocalization behaviors in a Dirac semimetal Cd3As2 thin flake device. At high temperatures, the phase coherence length lΦ first increases with decreasing temperature (T) and follows a power law dependence of lΦ ∝ T–0.4. Below ~3 K, lΦ tends to saturate to a value of ~180 nm. Another fitting parameter α, which is associated with independent transport channels, displays a logarithmic temperature dependence for T > 3 K, but also tends to saturate below ~3 K. The saturation value, ~1.45, is very close to 1.5, indicating three independent electron transport channels, which we interpret as due to decoupling of both the top and bottom surfaces as well as the bulk. This result, to our knowledge, provides first evidence that the surfaces and bulk states can become decoupled in electronic transport in Dirac semimetal Cd3As2.
Nanothermite NiO-Al is a promising material system for low gas emission heat sources; yet, its reactive properties are highly dependent on material processing conditions. In the current study, sputter deposition is used to fabricate highly controlled nanolaminates comprised of alternating NiO and Al layers. Films having an overall stoichiometry of 2Al to 3NiO were produced with different bilayer thicknesses to investigate how ignition and self-sustained, high temperature reactions vary with changes to nanometer-scale periodicity and preheat conditions. Ignition studies were carried out with both hot plate and laser irradiation and compared to slow heating studies in hot-stage x-ray diffraction. Ignition behavior has bilayer thickness and heating rate dependencies. The 2Al/3NiO with λ ≤ 300 nm ignited via solid/solid diffusion mixing (activation energy, Ea = 49 ± 3 kJ/mole). Multilayers having λ≥ 500 nm required a more favorable mixing kinetics of solid/liquid dissolution into molten Al (Ea = 30 ± 4 kJ/mole). This solid/liquid dissolution Ea is a factor of 5 lower than that of the previously reported powder compacts due to the elimination of a passivating Al oxide layer present on the powder. The reactant mixing mechanism between 300 and 500 nm bilayer thicknesses was dependent on the ignition source's heating rate. The self-propagating reaction velocities of 2Al/3NiO multilayers varied from 0.4 to 2.5 m/s. Pre-heating nanolaminates to temperatures below the onset reaction temperatures associated with forming intermediate nickel aluminides at multilayer interfaces led to increased propagation velocities, whereas pre-heating samples above the onset temperatures inhibited subsequent attempts at laser ignition.
Pulsed-power generators can produce well-controlled continuous ramp compression of condensed matter for high-pressure equation-of-state studies using the magnetic loading technique. X-ray diffraction (XRD) data from dynamically compressed samples provide direct measurements of the elastic compression of the crystal lattice, onset of plastic flow, strength–strain rate dependence, structural phase transitions, and density of crystal defects, such as dislocations. Here, we present a cost-effective, compact, pulsed x-ray source for XRD measurements on pulsed-power-driven ramp-loaded samples. This combination of magnetically driven ramp compression of materials with a single, short-pulse XRD diagnostic will be a powerful capability for the dynamic materials’ community to investigate in situ dynamic phase transitions critical to equation of states. Finally, we present results using this new diagnostic to evaluate lattice compression in Zr and Al and to capture signatures of phase transitions in CdS.
Niobium (Nb)-doped lead-tin-zirconate-titanate (PSZT) ceramics near the lead-zirconate-titanate 95/5 orthorhombic AFE-rhombohedral FE morphotropic phase boundary (PSZT 13.5/81/5.5 -1.6Nb) were prepared with up to 10 mol.% of hafnium (Hf) substituted for zirconium. The ceramics were prepared by a traditional solid-state synthesis route and sintered to near full density at 1150°C for 6 h in sealed alumina crucibles with self-same material as the lead vapor source. All compositions were ∼98% dense with no detectable secondary phases by X-ray diffraction. The grain size was ∼3 μm for all compositions, consisting of equiaxed grains with intergranular porosity. The compositions exhibited remnant polarization values of ∼32 μC/cm2. Depolarization by the hydrostatic pressure-induced FE-AFE phase transition occurred at 310 MPa for all compositions, resulting in a total depolarization output of 32.4 μC/cm2 for the PSZT ceramics. Evaluation of the R3c-R3m and R3m-Pm (Formula presented.) m phase transition temperatures by impedance spectroscopy showed temperatures on heating ranging from 86 to 92°C and 186 to 182°C, respectively, for increasing nominal Hf content. Thermal hysteresis of the phase transitions was also observed in the ceramics, with the transition temperature on cooling being 1–4°C lower. The study demonstrated that the PSZT ceramics are relatively insensitive to variations in Hf content in the range of 0 to 10 mol.%.
We report the formation of Al3Sc, in 100 nm Al0.8Sc0.2 films, is found to be driven by exposure to high temperature through higher deposition temperature or annealing. High film resistivity was observed in films with lower deposition temperature that exhibited a lack of crystallinity, which is anticipated to cause more electron scattering. An increase in deposition temperature allows for the nucleation and growth of crystalline Al3Sc regions that were verified by electron diffraction. The increase in crystallinity reduces electron scattering, which results in lower film resistivity. Annealing Al0.8Sc0.2 films at 600 °C in an Ar vacuum environment also allows for the formation and recrystallization of Al3Sc and Al and yields saturated resistivity values between 9.58 and 10.5 μΩ-cm regardless of sputter conditions. Al3Sc was found to nucleate and grow in a random orientation when deposited on SiO2, and highly {111} textured when deposited on 100 nm Ti and AlN films that were used as template layers. The rocking curve of the Al3Sc 111 reflection for the as-deposited films on Ti and AlN at 450 °C was 1.79° and 1.68°, respectively. Annealing the film deposited on the AlN template reduced the rocking curve substantially to 1.01° due to recrystallization of Al3Sc and Al within the film.
A rapid and facile design strategy to create a highly complex optical tag with programmable, multimodal photoluminescent properties is described. This was achieved via intrinsic and DNA-fluorophore hidden signatures. As a first covert feature of the tag, an intricate novel heterometallic near-infrared (NIR)-emitting mesoporous metal-organic framework (MOF) was designed and synthesized. The material is constructed from two chemically distinct, homometallic hexanuclear clusters based on Nd and Yb. Uniquely, the Nd-based cluster is observed here for the first time in a MOF and consists of two staggered Nd μ3-oxo trimers. To generate controlled, multimodal, and tailorable emission with difficult to counterfeit features, the NIR-emissive MOF was post-synthetically modified via a fluorescent DNA oligo labeling design strategy. The surface attachment of several distinct fluorophores, including the simultaneous attachment of up to three distinct fluorescently labeled oligos was achieved, with excitation and emission properties across the visible spectrum (480-800 nm). The DNA inclusion as a secondary covert element in the tag was demonstrated via the detection of SYBR Gold dye association. Importantly, the approach implemented here serves as a rapid and tailorable way to encrypt distinct information in a facile and modular fashion and provides an innovative technology in the quest toward complex optical tags.
Optical anticounterfeiting tags utilize the photoluminescent properties of materials to encode unique patterns, enabling identification and validation of important items and assets. These tags must combine optical complexity with ease of production and authentication to both prevent counterfeiting and to remain practical for widespread use. Metal-organic frameworks (MOFs) based on polynuclear, rare earth clusters are ideal materials platforms for this purpose, combining fine control over structure and composition, with tunable, complex energy transfer mechanisms via both linker and metal components. Here we report the design and synthesis of a set of heterometallic MOFs based on combinations of Eu, Nd, and Yb with the tetratopic linker 1,3,6,8-tetrakis(4-carboxyphenyl)pyrene. The energetics of this linker facilitate the intentional concealment of the visible emissions from Eu while retaining the infrared emissions of Nd and Yb, creating an optical tag with multiple covert elements. Unique to the materials system reported herein, we document the occurrence of a previously not observed 11-metal cluster correlated with the presence of Yb in the MOFs, coexisting with a commonly encountered 9-metal cluster. We demonstrate the utility of these materials as intricate optical tags with both rapid and in-depth screening techniques, utilizing orthogonal identifiers across composition, emission spectra, and emission decay dynamics. This work highlights the important effect of linker selection in controlling the resulting photoluminescent properties in MOFs and opens an avenue for the targeted design of highly complex, multifunctional optical tags.
Novel materials based on the aluminum oxyhydroxide boehmite phase were prepared using a glycothermal reaction in 1,4-butanediol. Under the synthesis conditions, the atomic structure of the boehmite phase is altered by the glycol solvent in place of the interlayer hydroxyl groups, creating glycoboehmite. The structure of glycoboehmite was examined in detail to determine that glycol molecules are intercalated in a bilayer structure, which would suggest that there is twice the expansion identified previously in the literature. This precursor phase enables synthesis of two new phases that incorporate either polyvinylpyrrolidone or hydroxylpropyl cellulose nonionic polymers. These new materials exhibit changes in morphology, thermal properties, and surface chemistry. All the intercalated phases were investigated using PXRD, HRSTEM, SEM, FT-IR, TGA/DSC, zeta potential titrations, and specific surface area measurement. These intercalation polymers are non-ionic and interact through wetting interactions and hydrogen bonding, rather than by chemisorption or chelation with the aluminum ions in the structure.
Solar thermochemical hydrogen (STCH) production is a promising method to generate carbon neutral fuels by splitting water utilizing metal oxide materials and concentrated solar energy. The discovery of materials with enhanced water-splitting performance is critical for STCH to play a major role in the emerging renewable energy portfolio. While perovskite materials have been the focus of many recent efforts, materials screening can be time consuming due to the myriad chemical compositions possible. This can be greatly accelerated through computationally screening materials parameters including oxygen vacancy formation energy, phase stability, and electron effective mass. In this work, the perovskite Gd0.5La0.5Co0.5Fe0.5O3 (GLCF), was computationally determined to be a potential water splitter, and its activity was experimentally demonstrated. During water splitting tests with a thermal reduction temperature of 1,350°C, hydrogen yields of 101 μmol/g and 141 μmol/g were obtained at re-oxidation temperatures of 850 and 1,000°C, respectively, with increasing production observed during subsequent cycles. This is a significant improvement from similar compounds studied before (La0.6Sr0.4Co0.2Fe0.8O3 and LaFe0.75Co0.25O3) that suffer from performance degradation with subsequent cycles. Confirmed with high temperature x-ray diffraction (HT-XRD) patterns under inert and oxidizing atmosphere, the GLCF mainly maintained its phase while some decomposition to Gd2-xLaxO3 was observed.
Laser beam directed energy deposition has become an increasingly popular advanced manufacturing technique for materials discovery as a result of the in situ alloying capability. In this study, we leverage an additive manufacturing enabled high throughput materials discovery approach to explore the composition space of a graded Wx(CoCrFeMnNi)100−x sample spanning 0 ≤ x ≤ 21 at%. In addition to microstructural and mechanical characterization, synchrotron high speed x-ray computer aided tomography was conducted on a W20(CoCrFeMnNi)80 composition to visualize melting dynamics, powder-laser interactions, and remelting effects of previously consolidated material. Results reveal the formation of the Fe7W6 intermetallic phase at W concentrations> 6 at%, despite the high configurational entropy. Unincorporated W particles also occurred at W concentrations> 10 at% accompanied by a dissolution band of Fe7W6 at the W/matrix interface and hardness values greater than 400 HV. The primary strengthening mechanism is attributed to the reinforcement of the Fe7W6 and W phases as a metal matrix composite. The in situ high speed x-ray imaging during remelting showed that an additional laser pass did not promote further mixing of the Fe7W6 or W phases suggesting that, despite the dissolution of the W into the Fe7W6 phase being thermodynamically favored, it is kinetically limited by the thickness/diffusivity of the intermetallic phase, and the rapid solidification of the laser-based process.
Zirconium-based metal-organic frameworks, including UiO-66 and related frameworks, have become the focus of considerable research in the area of chemical warfare agent (CWA) decontamination. However, little work has been reported exploring these metal-organic frameworks (MOFs) for CWA sensing applications. For many sensing approaches, the growth of high-quality thin films of the active material is required, and thin film growth methods must be compatible with complex device architectures. Several approaches to synthesize thin films of UiO-66 have been described but many of these existing methods are complex or time consuming. We describe the development of a simple and rapid microwave assisted synthesis of oriented UiO-66 thin films on unmodified silicon (Si) and gold (Au) substrates. Thin films of UiO-66 and UiO-66-NH2 can be grown in as little as 2 min on gold substrates and 30 min on Si substrates. The film morphology and orientation are characterized and the effects of reaction time and temperature on thin film growth on Au are investigated. Both reaction time and temperature impact the overgrowth of protruding discrete crystallites in the thin film layer but, surprisingly, no strong correlation is observed between film thickness and reaction time or temperature. We also briefly describe the synthesis of Zr/Ce solid solution thin films of UiO-66 on Au and report the first synthesis of a solid solution thin film MOF. Finally, we demonstrate the utility of the microwave method for the facile functionalization of two sensor architectures, plasmonic nanohole arrays and microresonators, with UiO-66 thin films.
This study relates structure, properties and thermodynamics, through synthesis, characterization and heat of formation measurements of rare earth iridate pyrochlore (RE2Ir2O7; RE = Y, Eu, Pr) crystalline powders. The RE2Ir2O7 phases are synthesized by high temperature solid-state synthesis methods. X-ray diffraction and elemental analysis techniques are utilized to validate the synthesis and enable structural comparisons. Trends in the bond angles indicate deviations from the Y and Eu analogs for the Pr2Ir2O7 phase. High temperature oxide melt solution calorimetry is used to determine the heats of formation of each phase. Breaking the trend expected across the rare earth series, the enthalpy of formation for Pr2Ir2O7 is more exothermic than the anticipated from the Y and Eu analogs.
We present progress on the synthesis of semimetal Cd3As2 by metal–organic chemical-vapor deposition (MOCVD). Specifically, we have optimized the growth conditions needed to obtain technologically useful growth rates and acceptable thin-film microstructures, with our studies evaluating the effects of varying the temperature, pressure, and carrier-gas type for MOCVD of Cd3As2 when performed using dimethylcadmium and tertiary-butylarsine precursors. In the course of the optimization studies, exploratory Cd3As2 growths are attempted on GaSb substrates, strain-relaxed InAs buffer layers grown on GaSb substrates, and InAs substrates. Notably, only the InAs-terminated substrate surfaces yield desirable results. Extensive microstructural studies of Cd3As2 thin films on InAs are performed by using multiple advanced imaging microscopies and x-ray diffraction modalities. The studied films are 5–75 nm in thickness and consist of oriented, coalesced polycrystals with lateral domain widths of 30–80 nm. The most optimized films are smooth and specular, exhibiting a surface roughness as low as 1.0 nm rms. Under cross-sectional imaging, the Cd3As2-InAs heterointerface appears smooth and abrupt at a lower film thickness, ~30 nm, but becomes quite irregular as the average thickness increases to ~55 nm. The films are strain-relaxed with a residual biaxial tensile strain (ϵxx = +0.0010) that opposes the initially compressive lattice-mismatch strain of Cd3As2 coherent on InAs (ϵxx = - 0.042). Importantly, phase-identification studies find a thin-film crystal structure consistent with the P42/nbc space group, placing MOCVD-grown Cd3As2 among the Dirac semimetals of substantial interest for topological quantum materials studies.
Ferroelectric phase stability in hafnium oxide is reported to be influenced by factors that include composition, biaxial stress, crystallite size, and oxygen vacancies. In the present work, the ferroelectric performance of atomic layer deposited Hf0.5Zr0.5O2 (HZO) prepared between TaN electrodes that are processed under conditions to induce variable biaxial stresses is evaluated. The post-processing stress states of the HZO films reveal no dependence on the as-deposited stress of the adjacent TaN electrodes. All HZO films maintain tensile biaxial stress following processing, the magnitude of which is not observed to strongly influence the polarization response. Subsequent composition measurements of stress-varied TaN electrodes reveal changes in stoichiometry related to the different preparation conditions. HZO films in contact with Ta-rich TaN electrodes exhibit higher remanent polarizations and increased ferroelectric phase fractions compared to those in contact with N-rich TaN electrodes. HZO films in contact with Ta-rich TaN electrodes also have higher oxygen vacancy concentrations, indicating that a chemical interaction between the TaN and HZO layers ultimately impacts the ferroelectric orthorhombic phase stability and polarization performance. The results of this work demonstrate a necessity to carefully consider the role of electrode processing and chemistry on performance of ferroelectric hafnia films.
Optical tags provide a way to quickly and unambiguously identify valuable assets. Current tag fluorophore options lack the tunability to allow combined methods of encoding in a single material. Herein we report a design strategy to encode multilayer complexity in a family of heterometallic rare-earth metal–organic frameworks based on highly connected nonanuclear clusters. To impart both intricacy and security, a synergistic approach was implemented resulting in both overt (visible) and covert (near-infrared, NIR) properties, with concomitant multi-emissive spectra and tunable luminescence lifetimes. Tag authentication is validated with a variety of orthogonal detection methodologies. Importantly, the effect induced by subtle compositional changes on intermetallic energy transfer, and thus on the resulting photophysical properties, is demonstrated. This strategy can be widely implemented to create a large library of highly complex, difficult-to-counterfeit optical tags.
Physical vapor deposition of organic explosives enables growth of polycrystalline films with a unique microstructure and morphology compared to the bulk material. This study demonstrates the ability to control crystal orientation and porosity in pentaerythritol tetranitrate films by varying the interfacial energy between the substrate and the vapor-deposited explosive. Variation in density, porosity, surface roughness, and optical properties is achieved in the explosive film, with significant implications for initiation sensitivity and detonation performance of the explosive material. Various surface science techniques, including angle-resolved X-ray photoelectron spectroscopy and multiliquid contact angle analysis, are utilized to characterize interfacial characteristics between the substrate and explosive film. Optical microscopy and scanning electron microscopy of pentaerythritol tetranitrate surfaces and fracture cross sections illustrate the difference in morphology evolution and the microstructure achieved through surface energy modification. X-ray diffraction studies with the Tilt-A-Whirl three-dimensional pole figure rendering and texture analysis software suite reveal that high surface energy substrates result in a preferred (110) out-of-plane orientation of pentaerythritol tetranitrate crystallites and denser films. Low surface energy substrates create more randomly textured pentaerythritol tetranitrate and lead to nanoscale porosity and lower density films. This work furthers the scientific basis for interfacial engineering of polycrystalline organic explosive films through control of surface energy, enabling future study of dynamic and reactive detonative phenomena at the microscale. Results of this study also have potential applications to active pharmaceutical ingredients, stimuli-responsive polymer films, organic thin film transistors, and other areas.
Germanium–antimony–telluride has emerged as a nonvolatile phase change memory material due to the large resistivity contrast between amorphous and crystalline states, rapid crystallization, and cyclic endurance. Improving thermal phase stability, however, has necessitated further alloying with optional addition of a quaternary species (e.g., C). In this work, the thermal transport implications of this additional species are investigated using frequency-domain thermoreflectance in combination with structural characterization derived from x-ray diffraction and Raman spectroscopy. Specifically, the room temperature thermal conductivity and heat capacity of (Ge2Sb2Te5)1–xCx are reported as a function of carbon concentration (x ≤ 0:12) and anneal temperature (T ≤ 350 °C) with results assessed in reference to the measured phase, structure, and electronic resistivity. Phase stability imparted by the carbon comes with comparatively low thermal penalty as materials exhibiting similar levels of crystallinity have comparable thermal conductivity despite the addition of carbon. The additional thermal stability provided by the carbon does, however, necessitate higher anneal temperatures to achieve similar levels of structural order.
High temperature operation of molten sodium batteries impacts cost, reliability, and lifetime, and has limited the widespread adoption of these grid-scale energy storage technologies. Poor charge transfer and high interfacial resistance between molten sodium and solid-state electrolytes, however, prevents the operation of molten sodium batteries at low temperatures. Here, in situ formation of tin-based chaperone phases on solid state NaSICON ion conductor surfaces is shown in this work to greatly improve charge transfer and lower interfacial resistance in sodium symmetric cells operated at 110 °C at current densities up to an aggressive 50 mA cm-2. It is shown that static wetting testing, as measured by the contact angle of molten sodium on NaSICON, does not accurately predict battery performance due to the dynamic formation of a chaperone NaSn phase during cycling. This work demonstrates the promise of sodium intermetallic-forming coatings for the advancement of low temperature molten sodium batteries by improved mating of sodium-NaSICON surfaces and reduced interfacial resistance.
The DOE R&D program under the Spent Fuel Waste Science Technology (SFWST) campaign has made key progress in modeling and experimental approaches towards the characterization of chemical and physical phenomena that could impact the long-term safety assessment of heat-generating nuclear waste disposition in deep clay/shale/argillaceous rock. International collaboration activities such as heater tests and postmortem analysis of samples recovered from these have elucidated key information regarding changes in the engineered barrier system (EBS) material exposed to years of thermal loads. Chemical and structural analyses of sampled bentonite material from such tests has as well as experiments conducted on these are key to the characterization of thermal effects affecting bentonite clay barrier performance and the extent of sacrificial zones in the EBS during the thermal period. Thermal, hydrologic, and chemical data collected from heater tests and laboratory experiments has been used in the development, validation, and calibration of THMC simulators to model near-field coupled processes. This information leads to the development of simulation approaches (e.g., continuum vs. discrete) to tackle issues related to flow and transport at various scales of the host-rock and EBS design concept. Consideration of direct disposal of large capacity dual-purpose canisters (DPCs) as part of the back-end SNF waste disposition strategy has generated interest in improving our understanding of the effects of elevated temperatures on the EBS design. This is particularly important for backfilled repository concepts where temperature plays a key role in the EBS behavior and long-term performance. This report describes multiple R&D efforts on disposal in argillaceous geologic media through development and application of coupled THMC process models, experimental studies on clay/metal/cement barrier and host-rock (argillite) material interactions, molecular dynamic (MD) simulations of water transport during (swelling) clay dehydration, first-principles studies of metaschoepite (UO2 corrosion product) stability, and advances in thermodynamic plus surface complexation database development. Drift-scale URL experiments provides key data for testing hydrological-chemical (HC) model involving strong couplings of fluid mixing and barrier material chemical interactions. The THM modeling focuses on heater test experiments in argillite rock and gas migration in bentonite as part of international collaboration activities at underground research laboratories (URLs). In addition, field testing at an URL involves in situ analysis of fault slip behavior and fault permeability. Pore-scale modeling of gas bubble migration is also being investigated within the gas migration modeling effort. Interaction experiments on bentonite samples from heater test under ambient and elevated temperatures permit the evaluation of ion exchange, phase stability, and mineral transformation changes that could impact clay swelling. Advances in the development, testing, and implementation of a spent nuclear fuel (SNF) degradation model coupled with canister corrosion focus on the effects of hydrogen gas generation and its integration with Geologic Disposal Safety Assessment (GDSA). GDSA integration activities includes evaluation of groundwater chemistries in shale formations.
Majorana zero modes (MZMs), fundamental building blocks for realizing topological quantum computers, can appear at the interface between a superconductor and a topological material. One of the experimental signatures that has been widely pursued to confirm the existence of MZMs is the observation of a large, quantized zero-bias conductance peak (ZBCP) in the differential conductance measurements. In this Letter, we report observation of such a large ZBCP in junction structures of normal metal (titanium/gold Ti/Au)-Dirac semimetal (cadmium-arsenide Cd3As2)-conventional superconductor (aluminum Al), with a value close to four times that of the normal state conductance. Our detailed analyses suggest that this large ZBCP is most likely not caused by MZMs. We attribute the ZBCP, instead, to the existence of a supercurrent between two far-separated superconducting Al electrodes, which shows up as a zero-bias peak because of the circuitry and thermal fluctuations of the supercurrent phase, a mechanism conceived by Ivanchenko and Zil'berman more than 50 years ago [Ivanchenko and Zil'berman, JETP 28, 1272 (1969)]. Our results thus call for extreme caution when assigning the origin of a large ZBCP to MZMs in a multiterminal semiconductor or topological insulator/semimetal setup. We thus provide criteria for identifying when the ZBCP is definitely not caused by an MZM. Furthermore, we present several remarkable experimental results of a supercurrent effect occurring over unusually long distances and clean perfect Andreev reflection features.
Residual strain in electrodeposited Li films may affect safety and performance in Li metal battery anodes, so it is important to understand how to detect residual strain in electrodeposited Li and the conditions under which it arises. To explore this Li films, electrodeposited onto Cu metal substrates, were prepared under an applied pressure of either 10 or 1000 kPa and subsequently tested for the presence or absence of residual strain via sin(ψ) analysis. X-ray diffraction (XRD) analysis of Li films required preparation and examination within an inert environment; hence, a Be-dome sample holder was employed during XRD characterization. Results show that the Li film grown under 1000 kPa displayed a detectable presence of in-plane compressive strain (-0.066%), whereas the Li film grown under 10 kPa displayed no detectable in-plane strain. The underlying Cu substrate revealed an in-plane residual strain near zero. Texture analysis via pole figure determination was also performed for both Li and Cu and revealed a mild fiber texture for Li metal and a strong bi-axial texture of the Cu substrate. Experimental details concerning sample preparation, alignment, and analysis of the particularly air-sensitive Li films have also been detailed. This work shows that Li metal exhibits residual strain when electrodeposited under compressive stress and that XRD can be used to quantify that strain.
A novel metal-organic framework (MOF), Mn-DOBDC, has been synthesized in an effort to investigate the role of both the metal center and presence of free linker hydroxyls on the luminescent properties of DOBDC (2,5-dihydroxyterephthalic acid) containing MOFs. Co-MOF-74, RE-DOBDC (RE-Eu and Tb), and Mn-DOBDC have been synthesized and analyzed by powder X-ray diffraction (PXRD) and the fluorescent properties probed by UV-Vis spectroscopy and density functional theory (DFT). Mn-DOBDC has been synthesized by a new method involving a concurrent facile reflux synthesis and slow crystallization, resulting in yellow single crystals in monoclinic space group C2/c. Mn-DOBDC was further analyzed by single-crystal X-ray diffraction (SCXRD), scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), and photoluminescent emission. Results indicate that the luminescent properties of the DOBDC linker are transferred to the three-dimensional structures of both the RE-DOBDC and Mn-DOBDC, which contain free hydroxyls on the linker. In Co-MOF-74 however, luminescence is quenched in the solid state due to binding of the phenolic hydroxyls within the MOF structure. Mn-DOBDC exhibits a ligand-based tunable emission that can be controlled in solution by the use of different solvents.
Development of calcium metal batteries has been historically frustrated by a lack of electrolytes capable of supporting reversible calcium electrodeposition. In this paper, we report the study of an electrolyte consisting of Ca(BH4)2 in tetrahydrofuran (THF) to gain important insight into the role of the liquid solvation environment in facilitating the reversible electrodeposition of this highly reactive, divalent metal. Through interrogation of the Ca2+ solvation environment and comparison with Mg2+ analogs, we show that an ability to reversibly electrodeposit metal at reasonable rates is strongly regulated by dication charge density and polarizability. Our results indicate that the greater polarizability of Ca2+ over Mg2+ confers greater configurational flexibility, enabling ionic cluster formation via neutral multimer intermediates. Increased concentration of the proposed electroactive species, CaBH4+, enables rapid and stable delivery of Ca2+ to the electrode interface. This work helps set the stage for future progress in the development of electrolytes for calcium and other divalent metal batteries.